Amanda Knox was en route to Seattle from Rome – a free woman whose conviction for murder had just been overturned – when David Thorne, the US ambassador to Italy, sent a cable to the State Department declaring that the case was officially over.

Thorne’s relief seemed palpable. Knox’s arrest, trial and imprisonment for the brutal slaying of her British housemate, Meredith Kercher, had dominated headlines all over the world, and was closely followed by American officials in Rome, diplomatic cables would later reveal. “Post considers this case closed,” he wrote in October 2011.

It turned out to be premature, but the depth of the ambassador’s miscalculation will only fully be known next week, when a highly-anticipated ruling in the ongoing case by Italy’s highest court could open the door to a whole new legal battle over Knox’s potential extradition from the US, a decision that would have significant diplomatic and political consequences from Rome to Washington DC.

Amanda Knox: I feel stranded and trapped since new guilty verdict

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Knox – who has been portrayed both as a maligned and naive innocent and as a sex-crazed psychopath – has already said she would have to be dragged “kicking and screaming” back to Italy. Many factors could influence the outcome of a potential extradition request. Even the decision of whether or not Knox wishes to have a child – she plans to marry a schoolfriend called Colin Sutherland – could become a factor in her forced return to the bel paese because American officials might delay the extradition of the mother of a small child. But the final decision – Italy’s to seek the extradition and the US’s to grant such a request – could ultimately hinge on politics, legal experts say.

The case has been long and complicated so far, with a series of drawn out decisions, appeals and reversals that are common in the notoriously slow and backlogged Italian justice system. Knox and her former boyfriend, Raffaele Sollecito, were convicted of Kercher’s murder in 2009, then freed on appeal two years later because of doubts about the veracity of physical evidence, including the alleged murder weapon found at Sollecito’s apartment. Both Knox and Sollecito have always maintained their innocence.

That acquittal was then thrown out of court in 2013 because the appeals court was ruled to have been inconsistent in its judgment of the evidence. A year later, after a retrial, the pair were found guilty – again – of murder, with Knox sentenced to 28 and a half years in prison, and Sollecito to 25 years.

Under Italian law, that decision will not be considered final unless and until it is upheld by the court of cassation in its ruling this week, which could come as soon as Wednesday. That is why Knox has been able to live freely in the US, even though she is currently considered guilty of murder in Italy. Sollecito is also free in Italy right now, but would be arrested immediately if the conviction were upheld.

If it does not uphold the conviction, the court could also decide to send one or both defendants back to trial, but it does not have the power to acquit Knox or Sollecito outright.

The pair knew one another for seven days prior to the murder. Their public canoodling shortly after Kercher’s body was discovered aroused suspicion at the time and fueled the perception – among those who believe they are guilty – that Knox, in particular, was a psychopath.

Though they are no longer a couple, the pair have faced justice together since their first interrogations by police in Perugia. That, too, could change this week. Sollecito’s attorney hinted last year that she would seek to exploit differences in their cases. “They’re not Siamese twins,” Giulia Bongiorno told reporters last year.

The court’s latest conviction relied on a written confession Knox made – and then later retracted – after being questioned by police, in which she said she had been in the house when the murder occurred but not participated in the crime, and that her boyfriend was not there. A third man, an Ivorian named Rudy Guede, was also convicted of murdering Kercher in 2008 after a fast-track trial. He has almost served half of his 16-year sentence. Although Sollecito has long maintained that both he and his former lover are innocent, his defence will now rely on the truthfulness of a confession that Knox has said was made under duress.

“If you believe in the confession, Sollecito is extraneous to the facts,” Bongiorno told the Guardian. “The words of Amanda Knox … exonerate Sollecito.”

Even if their convictions are upheld, the wheels of justice will continue to move slowly. After the court releases its legal rationale for the decision – which could take up to 90 days – the Italian minister of justice would then have up to six months to determine whether to demand Knox’s return from the US.

Michael Scadron, a former lawyer for the US Department of Justice and a keen observer of the Knox case, predicts the Italians would not seek extradition under pressure from the US. “They will use back channel diplomacy to prevent a request,” he says.

If such a request was nevertheless made, the US would technically have to abide by it under the strict terms of an extradition treaty between the countries.

“If the Italian supreme court sustains the conviction, it will be nearly impossible for the US – despite the political uproar that will occur among those who believe she is innocent – not to extradite her to Italy,” says Steve Clemons, a senior fellow at the New America Foundation and foreign policy expert. “Emotions may run high, but in the end the relations between Italy and the US are deep, strategic, complex, and are designed to respect each other’s laws, even in controversial cases,” he added.

Relations have not always been rosy, however. In 2001, diplomats from both sides had to duke out an agreement over a woman called Silvia Baraldini, an icon of the Italian left who had been convicted of bank robbery and kidnapping in the US but was released to Italy under the condition that she serve nine more years of her prison sentence. Baraldini was released early to be treated for cancer following tense negotiations in an episode that insiders say created mistrust between the parties.

Under US law, if an extradition request is made, it would be scrutinised by the State Department and then the Justice Department, and would then have to be approved by a US court, where Knox could appeal the extradition. If the courts approve of the request, the final decision rests with the US secretary of state, John Kerry.

It is far from clear on what grounds the US government could ultimately challenge a legal request. Some lawyers have said the fact that Knox was once acquitted of the crime, and then convicted, smacked of “double jeopardy”, the concept that a person cannot legally be tried twice for the same crime. Double jeopardy is specifically outlined as an exemption in the US-Italy extradition treaty, though it has never been tested in court.

Italian legal experts flatly reject that argument. They say Knox has not been charged in separate legal cases. She has gone through a single process that has not been particularly unusual in the multi-tiered Italian justice system, which the US agreed to respect.

Back in her home town of Seattle, Knox has begun tentatively to try to return to some semblance of a normal life. In the face of immense attention from journalists and paparazzi, she has kept a low profile. Last year, she started working for a local newspaper, the West Seattle Herald, writing features and theatre reviews. Her editor, Patrick Robinson, told the Daily Beast that he had approached her “to give her the opportunity of a normal life”.